It is well known to utilize a source of electrical power in order to speed the healing process in damaged bone and soft tissue. Through extensive research and development, it has been found that both electrical current and magnetic fields can play an important role in modifying tissue behavior. It is known that bone tissue generates its own electrical potentials during the healing process, and exposing the bone tissue to electrical energy at selected voltages and amperages can greatly enhance the speed of tissue regeneration.
Accordingly, a number of references disclose electrical implants that are used for various healing and regenerative purposes with respect to both bone and soft tissue. A typical electrical implant device includes probes or electrodes that are positioned adjacent the targeted tissue, and the electrodes are powered by an external power source, such as a subcutaneous battery. Discharged batteries must be replaced, and ultimately removed once the desired duration of electrical energy exposure has been achieved.
It is also known to utilize body fluids as an electrolyte in combination with anode and cathode elements implanted within the body to produce a galvanic cell capable of generating electrical potential for a specified treatment. Since the human body is mainly composed of water, even tissue and bone in contact with anode and cathode elements is sufficient for facilitating a galvanic reaction.
One early example of an electrical power source utilizing body fluids as an electrolyte is the U.S. Pat. No. 3,345,989. This reference discloses a pair of metal electrodes surgically implanted in body tissue in which one electrode acts as the anode and the other acts as the cathode. An implanted electronic device may close the circuit and therefore receive electrical power by use of insulated leads that extend from each electrode to the implanted device.
Another early example of an implanted device that acts as a bioelectric power supply is the invention found in the U.S. Pat. No. 3,421,512. This reference discloses an implanted pacemaker in which the electrical components are contained within a sealed housing formed by electrode plates that are sealed to one another. The electrode plates are made of selected materials to react with bodily fluids to form a galvanic power supply.
U.S. Pat. No. 3,353,539 discloses a biological power supply in which bodily fluid is used as the electrolyte to generate power from implanted electrodes. The electrodes are constructed of the similar metals resulting in production of electrical power.
U.S. Pat. No. 5,353,935 discloses a prosthetic implant for implantation into skeletal bone comprising an implantable base member having an internal housing surrounded partially by a porous wall, an anode secured in the internal housing in electrical contact with the porous wall, and a porous means placed in the internal housing for retaining a biocompatible electrolyte. When implanted into bone structure, the prosthetic implant generates sufficient current flow which results in in-vivo formation of calcium phosphate minerals between the implant and the surrounding bone, thereby, resulting in improved fixation and stability of the implant.
U.S. Pat. No. 5,725,377 discloses a dental implant that employs electrical bone growth stimulation by incorporating a galvanic cell in the implant. The implant is formed as a machine screw made of titanium. The machine screw contains an internal threaded portion for accommodating a cap screw to cover the top of the implant. The implant has a hollow portion with a small aluminum rivet pressed therein that makes intimate contact with the titanium implant. The rivet forms the anode of the cell which becomes the negative electrode of the battery. A slug of silver chloride is fastened to a cover screw. A saline solution is used as the electrolyte. Once activated, the reaction consists of the reduction of silver chloride to metallic silver. The slug of silver chloride forms the cathode of the cell and becomes the positive terminal of the battery.
U.S. Pat. No. 7,230,153 discloses a multi-layer conductive appliance having wound healing and analgesic properties. The appliance can be used as a wound dressing having at least one layer of a conductive material. When placed proximate to the portion of the body suffering from a pathologic condition, the dressing alters the electro-dynamic processes occurring in conjunction with the pathologic condition to promote healing and pain relief. The conductive material placed in contact with tissue surrounding the periphery of the wound and lowers the electrical potential and resistance of the wound thereby increasing wound current. Multi-laminate embodiments exhibit conductive material concentration gradients and a capacitive effect when sequential conductive layers are insulated by intervening non-conductive layers.
While it may be well known to provide a source of electrical power for enhancing tissue healing/regeneration, dedicated devices for generating electrical potential add to the overall cost and complexity of an orthopedic implant procedure. Furthermore, with respect to implanted batteries, the increased cost of using such batteries also results in a greater invasive procedure because the batteries must be separately implanted and monitored over time.
As orthopedic procedures continue to advance in the types and diversity of fixation devices used to repair damaged tissue, the cost of employing such fixation devices often becomes the limiting factor in whether the particular procedure can be conducted within cost limits allowed by the insurance carrier. The addition of a separate electrical generating device or a complex combination of an integral electrical generating device within a fixation device are not viable solutions in the present day medical care systems.
Therefore, there is a need to combine an orthopedic fixation device with an electrical energy source in a reliable, cost effective design. There is also a need to provide such a combination that has multiple potential uses for differing medical procedures without requiring complete re-design of the combination. There is also a need to provide such a combination that can deliver selected electrical energy parameters within a single implant. There is yet further a need to provide a fixation device that can be used also as an anchor for traditional sutures for repair of soft tissues, while the anchoring device can also perform its traditional function of anchoring the sutures.
These needs are satisfied with the present invention as described below with respect to preferred embodiments of the invention.